Experience shapes chandelier cell function and structure in the visual cortex

Detailed characterization of interneuron types in primary visual cortex (V1) has greatly contributed to understanding visual perception, yet the role of chandelier cells (ChCs) in visual processing remains poorly characterized. Using viral tracing we found that V1 ChCs predominantly receive monosynaptic input from local layer 5 pyramidal cells and higher-order cortical regions. Two-photon calcium imaging and convolutional neural network modeling revealed that ChCs are visually responsive but weakly selective for stimulus content. In mice running in a virtual tunnel, ChCs respond strongly to events known to elicit arousal, including locomotion and visuomotor mismatch. Repeated exposure of the mice to the virtual tunnel was accompanied by reduced visual responses of ChCs and structural plasticity of ChC boutons and axon initial segment length. Finally, ChCs only weakly inhibited pyramidal cells. These findings suggest that ChCs provide an arousal-related signal to layer 2/3 pyramidal cells that may modulate their activity and/or gate plasticity of their axon initial segments during behaviorally relevant events.

Axon Initial Segment GABA Inhibits Action Potential Generation throughout Periadolescent Development

Neurons are remarkably polarized structures: dendrites spread and branch to receive synaptic inputs while a single axon extends and transmits action potentials (APs) to downstream targets. Neuronal polarity is maintained by the axon initial segment (AIS), a region between the soma and axon proper that is also the site of action potential (AP) generation. This polarization between dendrites and axons extends to inhibitory neurotransmission. In adulthood, the neurotransmitter GABA hyperpolarizes dendrites but instead depolarizes axons. These differences in function collide at the AIS. Multiple studies have shown that GABAergic signaling in this region can share properties of either the mature axon or mature dendrite, and that these properties evolve over a protracted period encompassing periadolescent development. Here, we explored how developmental changes in GABAergic signaling affect AP initiation. We show that GABA at the axon initial segment inhibits action potential initiation in layer (L)2/3 pyramidal neurons in prefrontal cortex from mice of either sex across GABA reversal potentials observed in periadolescence. These actions occur largely through current shunts generated by GABAA receptors and changes in voltage-gated channel properties that affected the number of channels that could be recruited for AP electrogenesis. These results suggest that GABAergic neurons targeting the axon initial segment provide an inhibitory "veto" across the range of GABA polarity observed in normal adolescent development, regardless of GABAergic synapse reversal potential.Significance Statement GABA receptors are a major class of neurotransmitter receptors in the brain. Typically, GABA receptors inhibit neurons by allowing influx of negatively charged chloride ions into the cell. However, there are cases where local chloride concentrations promote chloride efflux through GABA receptors. Such conditions exist early in development in neocortical pyramidal cell axon initial segments (AISs), where action potentials (APs) initiate. Here, we examined how chloride efflux in early development interacts with mechanisms that support action potential initiation. We find that this efflux, despite moving membrane potential closer to action potential threshold, is nevertheless inhibitory. Thus, GABA at the axon initial segment is likely to be inhibitory for action potential initiation independent of whether chloride flows out or into neurons via these receptors.

Chandelier-Assisted Scleral Buckling: A Literature Review

The treatment of retinal detachment (RD) has seen numerous advancements in the last decades. Scleral buckling (SB) is a surgical procedure introduced in the 1950s that has seen a drastic reduction with the advent of vitrectomy. However, due to the new surgical visualization systems, SB has evolved and continues to be an extremely useful procedure in certain conditions. The presence of different case reports or interventional studies with comparable outcomes, as well as the lack of recent studies with direct comparison, may result in an underestimation of its potential nowadays. The aim of this review is to provide a comprehensive update on chandelier-assisted scleral bucking (CSB), with an overview of the surgical evolution, outcomes, advantages, and complications.

Inhibitory Circuits in the Basolateral Amygdala in Aversive Learning and Memory

Neural circuits in the basolateral amygdala (BLA) play a pivotal role in the learning and memory formation, and processing of emotionally salient experiences, particularly aversive ones. A diverse population of GABAergic neurons present in the BLA orchestrate local circuits to mediate emotional memory functions. Targeted manipulation of GABAergic neuronal subtypes has shed light on cell-type specific functional roles in the fear learning and memory, revealing organizing principles for the operation of inhibitory circuit motifs in the BLA.

A Tisket a Tasket: Chandelier ≠ Basket (Cell Bouton Density in Sclerotic DG)

GABA bouton subpopulations in the human dentate gyrus are differentially altered in mesial temporal lobe epilepsy Alhourani A, Fish KN, Wozny TA, Sudhakar V, Hamilton RL, Richardson RM. J Neuro . 2020;123(4):392-406. doi:10.1152/jn.00523.2018 Medically intractable temporal lobe epilepsy is a devastating disease, for which surgical removal of the seizure-onset zone is the only known cure. Multiple studies have found evidence of abnormal dentate gyrus network circuitry in human mesial temporal lobe epilepsy (MTLE). Principal neurons within the dentate gyrus gate entorhinal input into the hippocampus provide a critical step in information processing. Crucial to that role are GABA-expressing neurons, particularly parvalbumin (PV)-expressing basket cells (PVBCs) and chandelier cells (PVChCs), which provide strong, temporally coordinated inhibitory signals. Alterations in PVBC and PVChC boutons have been described in epilepsy, but the value of these studies has been limited due to methodological hurdles associated with studying human tissue. We developed a multilabel immunofluorescence confocal microscopy and a custom segmentation algorithm to quantitatively assess PVBC and PVChC bouton densities and to infer relative synaptic protein content in the human dentate gyrus. Using en bloc specimens from MTLE subjects with and without hippocampal sclerosis, paired with nonepileptic controls, we demonstrate the utility of this approach for detecting cell-type specific synaptic alterations. Specifically, we found increased density of PVBC boutons, while PVChC boutons decreased significantly in the dentate granule cell layer of subjects with hippocampal sclerosis compared with matched controls. In contrast, bouton densities for either PV-positive cell type did not differ between epileptic subjects without sclerosis and matched controls. These results may explain conflicting findings from previous studies that have reported both preserved and decreased PV bouton densities and establish a new standard for quantitative assessment of interneuron boutons in epilepsy.

Encircling Scleral Buckle with Chandelier Endoillumination and Endolaser for Repair of Rhegmatogenous Retinal Detachment

Purpose

To report a modified surgical technique for chandelier endoillumination-assisted scleral buckling using an endolaser.

Methods

A three patient case reports for demonstration of surgical technique.

Results

All patients underwent successful primary retinal detachment repair without any intraoperative or post-operative complications.

Conclusion

Endolaser can be employed during chandelier endoillumination assisted scleral buckling either as a standalone tool or in conjunction with cryopexy, especially in cases with posteriorly located retinal breaks.

Wide-angled endoillumination vs traditional scleral buckling surgery for retinal detachment - a comparative study

Purpose

To evaluate the surgical outcomes of traditional scleral buckling (TSB) compared to chandelier-assisted scleral buckling (CSB) for rhegmatogenous retinal detachment repair.

Patients and methods

A retrospective interventional comparative case series of 49 eyes that underwent SB procedure. Medical records of 27 and 22 eyes that underwent TSB and CSB surgery, respectively, were evaluated. Outcome measures included primary anatomical success, visual acuity (VA), and perioperative complications.

Results

Primary reattachment rate was similar with 85.2% in the TCB group and 81.8% in the CSB group (P=1.00); eight patients needed one additional operation or gas injection with a final reattachment rate of 100% at 6 months. Mean VA in the CSB group improved from 20/60 at presentation to 20/35, 6 months postoperatively. In the TSB group, VA improved from 20/80 to 20/45 (P=0.90). Among the eyes that were successfully reattached with either SB approach, two eyes in each group had cataract progression and none of them required surgery during follow-up. No cases of endophthalmitis were observed.

Conclusion

CSB is a modified technique with an advantage of superior visualization compared with the traditional surgery, which simplifies the operation, enhance competency, and could be used as a valuable educational tool. It can provide similar anatomical and functional outcomes with no additional perioperative complications.

Chandelier-assisted scleral buckling in an eye with longstanding inert foreign body with fresh rhegmatogenous retinal detachment

Intraocular foreign bodies (IOFBs) present in varied manners which in turn necessitate their removal in majority of the cases. A stone foreign body can remain inert inside the eye for years. Retinal detachment in eyes following penetrating trauma with an IOFB is common, but a combination of fresh rhegmatogenous retinal detachment in an eye with a longstanding inert stone foreign body is extremely rare. We report a case of a 50-year-old male with rhegmatogenous retinal detachment with a longstanding stone foreign body, where we managed such a scenario with a chandelier-assisted, sutureless, scleral buckle without removing the stone foreign body.

Endoillumination (chandelier) and wide-angle viewing-assisted fine-needle aspiration biopsy of intraocular mass lesions

Fine-needle aspiration biopsy (FNAB) of intraocular mass lesions is an important intervention in the presence of diagnostic difficulty. FNAB of intraocular mass lesions is also likely to become more commonly recommended for prognostication of tumors such as choroidal melanoma. The most commonly described approach for tumor localization and visualization during FNAB is transillumination and indirect ophthalmoscopic viewing. Herein, we report endoillumination (chandelier) and wide-angle viewing assisted, microscope-based approach for FNAB in two patients using two port minimally invasive vitreoretinal surgical approach. The submission is supported by a video demonstration. The entire procedure was completed under the microscope. Adequate sample was obtained. In the first patient, the inflammatory nature of the lesion was confirmed though magnetic resonance imaging had been reported as melanoma. In the second patient, a clinical diagnosis of amelanotic melanoma was confirmed. Endoillumination-assisted FNAB of intraocular mass lesions is easier to learn and more precise and hence carries lesser risks.

Outcomes of scleral buckling using chandelier endoillumination

PURPOSE

To report the results and complications of scleral buckling for the treatment of rhegmatogenous retinal detachment (RRD) using 25-gauge chandelier endoillumination.

METHODS

A total of 61 patients (61 eyes) with RRD were treated with scleral buckling. For the sclera buckling procedure, a 25-gauge chandelier was inserted through the pars plana for intra-ocular illumination, and retinal tears were identified and treated with episcleral cryotherapy under surgical microscope. On postoperative days 1, 3 and 7, the intra-ocular pressure was measured by a non-contact tonometer. On postoperative months 1 and 3, ultrasound biomicroscopy was used to examine the pars plana incision.

RESULTS

In the surgical procedure, there was no lenticular or retinal damage due to the chandelier insertion. There was no conjunctival bleb formation at pars plana incision and no incidence of endophthalmitis after surgery. The mean intra-ocular pressure was 15.74 ± 2.98, 15.83 ± 2.76 and 16.14 ± 2.52 mmHg on postoperative days 1, 3 and 7, respectively. The one-time retinal reattachment rate was 93.4%. No visible vitreous incarceration was found in the incision of the pars plana.

CONCLUSION

There was no complication found due to the chandelier insertion in early postoperative period. Chandelier endoillumination is a feasible method for retinal visualization under surgical microscope during scleral buckling.

Periadolescent Maturation of GABAergic Hyperpolarization at the Axon Initial Segment

Neuronal chloride levels are developmentally regulated. Early in life, high intracellular concentrations support chloride efflux and depolarization at GABAergic synapses. In mouse, intracellular chloride decreases over the first postnatal week in the somatodendritic compartment, eventually supporting mature, hyperpolarizing GABAergic inhibition. In contrast to this dendritic switch, it is less clear how GABAergic signaling at the axon initial segment (AIS) functions in mature pyramidal cells, as reports of both depolarization and hyperpolarization have been reported in the AIS past the first postnatal week. Here, we show that GABAergic signaling at the AIS of prefrontal pyramidal cells, indeed, switches polarity from depolarizing to hyperpolarizing but does so over a protracted periadolescent period. This is the most delayed maturation in chloride reversal in any structure studied to date and suggests that chandelier cells, which mediate axo-axonic inhibition, play a unique role in the periadolescent maturation of prefrontal circuits.